Currently two methods of making high-value products via Fischer-Tropsch synthesis are predominately utilized. The first, a high temperature Fischer-Tropsch synthesis, makes a high fraction of olefins in the product, but also makes a large variety of olefin, paraffin, naphthene, aromatic, alcohol, aldehyde, carboxylic acid and carboxylic ester isomers. The separation of all these isomers is extremely difficult and involves a number of steps, including, but not limited to, isomeric distillation, solvent extraction, and extractive distillation. The second process, a low temperature Fischer-Tropsch synthesis produces primarily normal paraffins solvents, naphthas, and waxes. A number of processes to hydrocrack and hydroisomerize Fischer-Tropsch waxes into a variety of isoparaffin products such as isoparaffin solvents, naphthas, and lubricant basestocks are known n the art. However, many of the high-volume, high-value olefin and alcohol applications require high linearity or specific branching of the olefin and/or alcohol products. Such highly linear or specifically branched olefins and alcohols are very difficult to separate from high-temperature Fischer-Tropsch products. Moreover, no viable processes for isolating such alcohols and olefins from low-temperature Fischer-Tropsch products are known.
One characteristic of one low temperature Fischer-Tropsch process is the high degree of linearity of the product hydrocarbons. Moreover, where the product is not entirely linear, the branching is predominately specifically monomethyl and terminal. As used herein, the term “terminal” indicates a location at the second or third carbon from the end of the chain. Such low temperature Fischer-Tropsch process is described in the commonly-owned co-pending U.S. application Ser. Nos. 10/426,154, which is incorporated herein by reference. Depending on the carbon number, between about 30% to about 90% of the product may be composed of normal paraffins, and less than about 15%, but most likely less than about 5% of each carbon number component may be the methyl-branched iso-paraffins.
The olefin content of the low temperature Fischer-Tropsch synthesis product may range from as high as 50% at C4 with as much as about 40% being alpha-olefins and about 10% being internal olefins. Conversely, at C14, the total olefins may be 10% or less, with less than 5% internal olefins. In addition to normal paraffins, isoparaffins, and olefins, such low temperature Fischer-Tropsch process generally produces from between about 5 to about 15% oxygenates, depending on the carbon number. The oxygenates are predominantly primary alcohols.